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JS function to generate random number or random string

Saturday, April 30, 2011

Javascript function to generate random number

Javascript random number generation function is Math.random()

alert(Math.random()); // returns number like 0.3871769046200184

The above JavaScript statement returns a random number between 0 and 1


var randnum=Math.floor(Math.random()*1001);

This will generate a random number between 0 and 1001


var randnum=Math.floor(Math.random()*101);

This will generate a random number between 0 and 101


Function to generate a random number from the set of whole number { 0,1,2,3,----,n }

Copy the code and save as a .html file and run on your browser


<h1>Random number from { 0,1,2,3,----,n}</h1>
<p>Click the button to display a random number from the set of whole numbers { 0,1,2,3,----,n }.</p>
<p id="demo"></p>

<button type="button" onclick="myFunction(5)">Try it</button>

function myFunction(maxVal)
var randVal = Math.random()*maxVal;



function randomXToY(minVal,maxVal,floatVal)
var randVal = minVal+(Math.random()*(maxVal-minVal));
return typeof floatVal=='undefined'?Math.round(randVal):randVal.toFixed(floatVal);

The above JavaScript funciton accepts three parameters.The first and second parameter is mandatory while the third is optional. The first and second parameter specifies the range between which the random number has to be generated. The thir parameter is optional which specifies number of floating point digits, if not provided, the above JavaScript function returns integer random number.


//function to get random number from 1 to n

function randomToN(maxVal,floatVal)
var randVal = Math.random()*maxVal;
return typeof floatVal=='undefined'?Math.round(randVal):randVal.toFixed(floatVal);

In the above JavaScript function, there are two parameters. One for the maximum value(N) up to which random number have to be generated. The second parameter is optional which specifies number of digits after decimal point.If not provided, this function returns integer.


function randomString(len) {
if(!len) len=5;
var chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz";
var string_length = len;
var randomstring = '';
for (var i=0; i<string_length; i++) {
var rnum = Math.floor(Math.random() * chars.length);
randomstring += chars.substring(rnum,rnum+1);
return randomstring;


The above function will generate a random string, here you have to pass the number of character that should be present in the resulting random string.

call like randomString(5) : thsi call will generate a random string with 5 characters.

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